This invention relates to fabricated tubular or box-shaped structural members such as a horizontal beam or a vertical column and of the general type disclosed in U.S. Pat. Nos. 3,999,354 and 4,580,380 which disclose two different forms of fabricated box beams. In the construction of such a structural member, it is not only desirable to provide a member which may be economically constructed and with a high strength/weight ratio, it is also desirable for the construction to provide flexibility so that the member may be conveniently constructed in different sizes and/or shapes according to the structural loading. It is also desirable for the structural member to have moisture and corrosion resistance so that the member has a long service life and requires no significant maintenance.